NSC LM3420AM5-12.6 Lithium-ion battery charge controller Datasheet

LM3420-4.2, -8.2, -8.4, -12.6, -16.8
Lithium-Ion Battery Charge Controller
General Description
The LM3420 series of controllers are monolithic integrated
circuits designed for charging and end-of-charge control for
Lithium-Ion rechargeable batteries. The LM3420 is available
in five fixed voltage versions for one through four cell charger
applications (4.2V, 8.2V/8.4V, 12.6V and 16.8V respectively).
Included in a very small package is an (internally compensated) op amp, a bandgap reference, an NPN output transistor, and voltage setting resistors. The amplifier’s inverting input is externally accessible for loop frequency
compensation. The output is an open-emitter NPN transistor
capable of driving up to 15 mA of output current into external
circuitry.
A trimmed precision bandgap reference utilizes temperature
drift curvature correction for excellent voltage stability over
the operating temperature range. Available with an initial tolerance of 0.5% for the A grade version, and 1% for the standard version, the LM3420 allows for precision end-of-charge
control for Lithium-Ion rechargeable batteries.
The LM3420 is available in a sub-miniature 5-lead SOT23-5
surface mount package thus allowing very compact designs.
Features
n
n
n
n
n
Voltage options for charging 1, 2, 3 or 4 cells
Tiny SOT23-5 package
Precision (0.5%) end-of-charge control
Drive capability for external power stage
Low quiescent current, 85 µA (typ.)
Applications
n Lithium-Ion battery charging
n Suitable for linear and switching regulator charger
designs
Typical Application and Functional Diagram
DS012359-1
Typical Constant Current/Constant Voltage
Li-Ion Battery Charger
DS012359-2
LM3420 Functional Diagram
SIMPLE SWITCHER ® is a registered trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation
DS012359
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LM3420-4.2, -8.2, -8.4, -12.6, -16.8 Lithium-Ion Battery Charge Controller
July 2000
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Connection Diagrams and Order Information
5-Lead Small Outline Package (M5)
Actual Size
DS012359-4
DS012359-3
*No internal connection, but should be soldered to PC board for best heat
transfer.
Top View
For Ordering Information
See Figure 1 in this Data Sheet
See NS Package Number MF05A
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2
ESD Susceptibility (Note 3)
Human Body Model
1500V
See AN-450 “Surface Mounting Methods and Their Effect
on Product Reliability” for methods on soldering
surface-mount devices.
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage V(IN)
Output Current
Junction Temperature
Storage Temperature
Lead Temperature
Vapor Phase (60 seconds)
Infrared (15 seconds)
Power Dissipation (TA = 25˚C)
(Note 2)
20V
20 mA
150˚C
−65˚C to +150˚C
Operating Ratings (Notes 1, 2)
Ambient Temperature Range
Junction Temperature Range
Output Current
+215˚C
+220˚C
−40˚C ≤ TA ≤ +85˚C
−40˚C ≤ TJ ≤ +125˚C
15 mA
300 mW
LM3420-4.2
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
VREG
Parameter
Regulation Voltage
Regulation Voltage
Conditions
IOUT = 1 mA
Typical
LM3420A-4.2
LM3420-4.2
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
4.221/4.242
4.242/4.284
4.179/4.158
4.158/4.116
V(min)
± 0.5/ ± 1
± 1/ ± 2
%(max)
4.2
IOUT = 1 mA
V
V(max)
Tolerance
Iq
Quiescent Current
IOUT = 1 mA
85
Gm
Transconductance
20 µA ≤ IOUT ≤ 1 mA
3.3
∆IOUT/∆VREG
VOUT = 2V
1 mA ≤ IOUT ≤ 15 mA
Voltage Gain
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
∆VOUT/∆VREG
RL = 200Ω (Note 6)
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
Output Saturation
(Note 7)
IOUT = 15 mA
IL
Output Leakage
V(IN) = VREG −100 mV
Current
VOUT = 0V
Rf
V(IN) = VREG +100 mV
1.3/0.75
1.0/0.50
mA/mV(min)
3.0/1.5
2.5/1.4
mA/mV(min)
550/250
450/200
V/V(min)
1500/900
1000/700
V/V(min)
mA/mV
mA/mV
V/V
V/V
1.0
V
1.2/1.3
1.2/1.3
V(max)
0.5/1.0
0.5/1.0
µA(max)
94
94
kΩ(max)
56
56
kΩ(min)
0.1
Internal Feedback
Output Noise
µA(max)
3500
µA
75
Resistor (Note 8)
En
125/150
1000
RL = 2 kΩ
VSAT
110/115
6.0
VOUT = 2V
AV
µA
IOUT = 1 mA, 10 Hz ≤ f ≤ 10 kHz
70
kΩ
µVRMS
Voltage
3
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Absolute Maximum Ratings (Note 1)
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
LM3420-8.2
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
VREG
Parameter
Regulation Voltage
Regulation Voltage
Conditions
IOUT = 1 mA
Typical
LM3420A-8.2
LM3420-8.2
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
8.241/8.282
8.282/8.364
8.159/8.118
8.118/8.036
V(min)
± 0.5/ ± 1
± 1/ ± 2
%(max)
110/115
125/150
µA(max)
1.3/0.75
1.0/0.50
mA/mV(min)
3.0/1.5
2.5/1.4
mA/mV(min)
550/250
450/200
V/V(min)
8.2
IOUT = 1 mA
V
V(max)
Tolerance
Iq
Quiescent Current
Gm
IOUT = 1 mA
Transconductance
20 µA ≤ IOUT ≤ 1 mA
∆IOUT/∆VREG
VOUT = 6V
85
3.3
1 mA ≤ IOUT ≤ 15 mA
Voltage Gain
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
∆VOUT/∆VREG
RL = 470Ω (Note 6)
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
IL
Rf
Output Saturation
V(IN) = VREG +100 mV
(Note 7)
IOUT = 15 mA
Output Leakage
V(IN) = VREG −100 mV
Current
VOUT = 0V
V/V
1500/900
1000/700
V/V(min)
1.2/1.3
1.2/1.3
V(max)
0.5/1.0
0.5/1.0
µA(max)
220
220
kΩ(max)
132
132
kΩ(min)
1.0
V
0.1
Internal Feedback
Output Noise
V/V
3500
µA
176
Resistor (Note 8)
En
mA/mV
1000
RL = 5 kΩ
VSAT
mA/mV
6.0
VOUT = 6V
AV
µA
IOUT = 1 mA, 10 Hz ≤ f ≤ 10 kHz
kΩ
140
µVRMS
Voltage
LM3420-8.4
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
VREG
Parameter
Regulation Voltage
Regulation Voltage
Conditions
IOUT = 1 mA
Typical
LM3420A-8.4
LM3420-8.4
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
8.442/8.484
8.484/8.568
V(max)
8.358/8.316
8.316/8.232
V(min)
± 0.5/ ± 1
± 1/ ± 2
%(max)
8.4
IOUT = 1 mA
V
Tolerance
Iq
Quiescent Current
IOUT = 1 mA
85
Gm
Transconductance
20 µA ≤ IOUT ≤ 1 mA
3.3
∆IOUT/∆VREG
VOUT = 6V
1 mA ≤ IOUT ≤ 15 mA
110/115
125/150
µA(max)
1.3/0.75
1.0/0.50
mA/mV(min)
mA/mV
6.0
VOUT = 6V
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µA
mA/mV
3.0/1.5
4
2.5/1.4
mA/mV(min)
(Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
AV
Parameter
Conditions
Voltage Gain
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
∆VOUT/∆VREG
RL = 470Ω (Note 6)
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
Typical
LM3420A-8.4
LM3420-8.4
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
1000
IL
Rf
Output Saturation
V(IN) = VREG +100 mV
(Note 7)
IOUT = 15 mA
Output Leakage
V(IN) = VREG −100 mV
Current
VOUT = 0V
V/V(min)
1500/900
1000/700
V/V(min)
1.2/1.3
1.2/1.3
V(max)
0.5/1.0
0.5/1.0
µA(max)
227
227
kΩ(max)
135
135
kΩ(min)
V/V
V
0.1
Internal Feedback
Output Noise
450/200
1.0
µA
181
Resistor (Note 8)
En
550/250
3500
RL = 5 kΩ
VSAT
V/V
IOUT = 1 mA, 10 Hz ≤ f ≤ 10 kHz
kΩ
140
µVRMS
Voltage
LM3420-12.6
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
VREG
Parameter
Regulation Voltage
Regulation Voltage
Conditions
IOUT = 1 mA
Typical
LM3420A-12.6
LM3420-12.6
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
12.6
IOUT = 1 mA
V
12.663/12.726
12.726/12.852
12.537/12.474
12.474/12.348
V(max)
V(min)
± 0.5/ ± 1
± 1/ ± 2
%(max)
110/115
125/150
µA(max)
1.3/0.75
1.0/0.5
mA/mV(min)
3.0/1.5
2.5/1.4
mA/mV(min)
550/250
450/200
V/V(min)
Tolerance
Iq
Gm
Quiescent Current
IOUT = 1 mA
Transconductance
20 µA ≤ IOUT ≤ 1 mA
∆IOUT/∆VREG
VOUT = 10V
85
3.3
1 mA ≤ IOUT ≤ 15 mA
Voltage Gain
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
∆VOUT/∆VREG
RL = 750Ω (Note 6)
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
Output Saturation
V(IN) = VREG +100 mV
(Note 7)
IOUT = 15 mA
IL
Output Leakage
V(IN) = VREG −100 mV
Current
VOUT = 0V
Rf
Internal Feedback
Output Noise
Voltage
V/V
3500
V/V
1500/900
1000/700
V/V(min)
1.2/1.3
1.2/1.3
V(max)
1.0
V
0.1
µA
0.5/1.0
0.5/1.0
µA(max)
359
359
kΩ(max)
215
215
kΩ(min)
287
Resistor (Note 8)
En
mA/mV
1000
RL = 10 kΩ
VSAT
mA/mV
6.0
VOUT = 10V
AV
µA
IOUT = 1 mA, 10 Hz ≤ f ≤ 10 kHz
5
210
kΩ
µVRMS
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
LM3420-8.4
Electrical Characteristics
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
LM3420-16.8
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, V(IN) = VREG, VOUT = 1.5V.
Symbol
VREG
Parameter
Regulation Voltage
Regulation Voltage
Conditions
IOUT = 1 mA
Typical
LM3420A-16.8
LM3420-16.8
Units
(Note 4)
Limit
Limit
(Limits)
(Note 5)
(Note 5)
16.884/16.968
16.968/17.136
16.716/16.632
16.632/16.464
V(min)
± 0.5/ ± 1
± 1/ ± 2
%(max)
110/115
125/150
µA(max)
0.8/0.4
0.7/0.35
mA/mV(min)
2.9/0.9
2.5/0.75
mA/mV(min)
550/250
450/200
V/V(min)
16.8
V
IOUT = 1 mA
V(max)
Tolerance
Iq
Quiescent Current
Gm
IOUT = 1 mA
Transconductance
20 µA ≤ IOUT ≤ 1 mA
∆IOUT/∆VREG
VOUT = 15V
85
3.3
1 mA ≤ IOUT ≤ 15 mA
Voltage Gain
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
∆VOUT/∆VREG
RL = 1 kΩ (Note 6)
1V ≤ VOUT ≤ VREG − 1.2V (−1.3)
IL
Rf
Output Saturation
V(IN) = VREG +100 mV
(Note 7)
IOUT = 15 mA
Output Leakage
V(IN) = VREG −100 mV
Current
VOUT = 0V
V/V
1200/750
1000/650
V/V(min)
1.2/1.3
1.2/1.3
V(max)
0.5/1.0
0.5/1.0
µA(max)
490
490
kΩ(max)
294
294
kΩ(min)
1.0
V
0.1
Internal Feedback
Output Noise
Voltage
V/V
3500
µA
392
Resistor (Note 8)
En
mA/mV
1000
RL = 15 kΩ
VSAT
mA/mV
6.0
VOUT = 15V
AV
µA
IOUT = 1 mA, 10 Hz ≤ f ≤ 10 kHz
kΩ
280
µVRMS
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The
guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed
test conditions.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to ambient thermal resistance), and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PDmax = (TJmax − TA)/θJA or the number
given in the Absolute Maximum Ratings, whichever is lower. The typical thermal resistance (θJA) when soldered to a printed circuit board is approximately 306˚C/W
for the M5 package.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.
Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Averaging Outgoing Quality Level (AOQL).
Note 6: Actual test is done using equivalent current sink instead of a resistor load.
Note 7: VSAT = V(IN) − VOUT, when the voltage at the IN pin is forced 100 mV above the nominal regulating voltage (VREG).
Note 8: See Applications and Typical Performance Characteristics sections for information on this resistor.
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6
4.2V
Bode Plot
Response Time
for 4.2V Version
Response Time
for 4.2V Version
DS012359-17
8.2V and 8.4V
Bode Plot
DS012359-18
Response Time for
8.2V, 8.4V Versions
DS012359-20
12.6V
Bode Plot
Response Time for
8.2V, 8.4V Versions
DS012359-21
Response Time
for 12.6V Version
DS012359-22
Response Time
for 12.6V Version
DS012359-23
16.8V
Bode Plot
DS012359-19
DS012359-24
Response Time
for 16.8V Version
DS012359-25
Response Time
for 16.8V Version
DS012359-26
DS012359-27
7
DS012359-28
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Typical Performance Characteristics
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Typical Performance Characteristics
Regulation Voltage vs
Output Voltage and
Load Resistance
(Continued)
Circuit Used for Bode Plots
Circuit Used for Response Time
DS012359-30
DS012359-31
DS012359-29
Regulation Voltage vs
Output Voltage and
Load Resistance
Internal Feedback
Resistor (Rf)
Tempco
Quiescent Current
DS012359-33
DS012359-32
Regulation Voltage vs
Output Voltage and
Load Resistance
DS012359-34
Normalized
Temperature Drift
Output Saturation
Voltage (VSAT)
DS012359-36
DS012359-35
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8
DS012359-37
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Typical Performance Characteristics
(Continued)
Regulation Voltage vs
Output Voltage and
Load Resistance
DS012359-38
9
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Five Lead Surface Mount Package Information
The small SOT23-5 package allows only 4 alphanumeric characters to identify the product. The table below contains the field information marked on the package.
Voltage
Grade
Order
Package
Information
Marking
Supplied as
4.2V
A (Prime)
LM3420AM5-4.2
D02A
1000 unit increments on tape and reel
4.2V
A (Prime)
LM3420AM5X-4.2
D02A
3000 unit increments on tape and reel
4.2V
B (Standard)
LM3420M5-4.2
D02B
1000 unit increments on tape and reel
4.2V
B (Standard)
LM3420M5X-4.2
D02B
3000 unit increments on tape and reel
8.2V
A (Prime)
LM3420AM5-8.2
D07A
1000 unit increments on tape and reel
8.2V
A (Prime)
LM3420AM5X-8.2
D07A
3000 unit increments on tape and reel
8.2V
B (Standard)
LM3420M5-8.2
D07B
1000 unit increments on tape and reel
8.2V
B (Standard)
LM3420M5X-8.2
D07B
3000 unit increments on tape and reel
8.4V
A (Prime)
LM3420AM5-8.4
D03A
1000 unit increments on tape and reel
8.4V
A (Prime)
LM3420AM5X-8.4
D03A
3000 unit increments on tape and reel
8.4V
B (Standard)
LM3420M5-8.4
D03B
1000 unit increments on tape and reel
8.4V
B (Standard)
LM3420M5X-8.4
D03B
3000 unit increments on tape and reel
12.6V
A (Prime)
LM3420AM5-12.6
D04A
1000 unit increments on tape and reel
12.6V
A (Prime)
LM3420AM5X-12.6
D04A
3000 unit increments on tape and reel
12.6V
B (Standard)
LM3420M5-12.6
D04B
1000 unit increments on tape and reel
12.6V
B (Standard)
LM3420M5X-12.6
D04B
3000 unit increments on tape and reel
16.8V
A (Prime)
LM3420AM5-16.8
D05A
1000 unit increments on tape and reel
16.8V
A (Prime)
LM3420AM5X-16.8
D05A
3000 unit increments on tape and reel
16.8V
B (Standard)
LM3420M5-16.8
D05B
1000 unit increments on tape and reel
16.8V
B (Standard)
LM3420M5X-16.8
D05B
3000 unit increments on tape and reel
FIGURE 1. SOT23-5 Marking
The first letter “D” identifies the part as a Driver, the next two numbers indicate the voltage, “02” for a 4.2V part, “07” for an 8.2V
part, “03” for an 8.4V part, “04” for a 12.6V part, and “05” for a 16.8V part. The fourth letter indicates the grade, “B” for standard
grade, “A” for the prime grade.
The SOT23-5 surface mount package is only available on tape in quantity increments of 1000 on tape and reel (indicated by the
letters “M5” in the part number), or in quantity increments of 3000 on tape and reel (indicated by the letters “M5X” in the part number).
single capacitor (CC) connected from the compensation pin
to the out pin of the LM3420. The capacitor values shown in
the schematics are adequate under most conditions, but
they can be increased or decreased depending on the desired loop response. Applying a load pulse to the output of a
regulator circuit and observing the resultant output voltage
response is an easy method of determining the stability of
the control loop.
Analyzing more complex feedback loops requires additional
information.
The formula for AC gain at a frequency (f) is as follows;
Product Description
The LM3420 is a shunt regulator specifically designed to be
the reference and control section in an overall feedback loop
of a Lithium-Ion battery charger. The regulated output voltage is sensed between the IN pin and GROUND pin of the
LM3420. If the voltage at the IN pin is less than the LM3420
regulating voltage (VREG), the OUT pin sources no current.
As the voltage at the IN pin approaches the VREG voltage,
the OUT pin begins sourcing current. This current is then
used to drive a feedback device (opto-coupler), or a power
device (linear regulator, switching regulator, etc.), which servos the output voltage to be the same value as VREG.
In some applications, (even under normal operating conditions) the voltage on the IN pin can be forced above the
VREG voltage. In these instances, the maximum voltage applied to the IN pin should not exceed 20V. In addition, an external resistor may be required on the OUT pin to limit the
maximum current to 20 mA.
where Rf ≈ 75 kΩ for the 4.2V part, Rf ≈ 181 kΩ for the 8.4V
part, Rf ≈ 287 kΩ for the 12.6V part, and Rf ≈ 392 kΩ for the
16.8V part.
The resistor (Rf) in the formula is an internal resistor located
on the die. Since this resistor value will affect the phase margin, the worst case maximum and minimum values are im-
Compensation
The inverting input of the error amplifier is brought out to allow overall closed-loop compensation. In many of the applications circuits shown here, compensation is provided by a
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10
Test Circuit
(Continued)
The test circuit shown in Figure 2 can be used to measure
and verify various LM3420 parameters. Test conditions are
set by forcing the appropriate voltage at the VOUT Set test
point and selecting the appropriate RL or IOUT as specified in
the Electrical Characteristics section. Use a DVM at the
“measure” test points to read the data.
portant when analyzing closed loop stability. The minimum
and maximum room temperature values of this resistor are
specified in the Electrical Characteristics section of this data
sheet, and a curve showing the temperature coefficient is
shown in the curves section. Minimum values of Rf result in
lower phase margins.
DS012359-7
FIGURE 2. LM3420 Test Circuit
VREG External Voltage Trim
The regulation voltage (VREG) of the LM3420 can be externally trimmed by adding a single resistor from the COMP pin
to the +IN pin or from the COMP pin to the GND pin, depending on the desired trim direction. Trim adjustments up to
± 10% of VREG can be realized, with only a small increase in
the temperature coefficient. (See temperature coefficient
curve shown in Figure 3 below.)
DS012359-9
Increasing VREG
DS012359-10
Decreasing VREG
FIGURE 4. Changing VREG
Formulas for selecting trim resistor values are shown below,
based on the percent of increase (%incr) or percent of decrease (%decr) of the output voltage from the nominal voltage.
For LM3420-4.2
Rincrease = 22x105/%incr
DS012359-8
Normalized Temperature Drift with
Output Externally Trimmed
Rdecrease = (53x105/%decr) − 75x103
For LM3420-8.2
11
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Compensation
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
VREG External Voltage Trim
cuits shown are designed for 2 cell operation, but they can
readily be changed for either 1, 3 or 4 cell charging applications.
(Continued)
Rincrease = 26x105/%incr
Rdecrease = (150x105/%decr) − 176x103
One item to keep in mind when designing with the LM3420 is
that there are parasitic diodes present. In some designs, under special electrical conditions, unwanted currents may
flow. Parasitic diodes exist from OUT to IN, as well as from
GROUND to IN. In both instances the diode arrow is pointed
toward the IN pin.
For LM3420-8.4
Rincrease = 26x105/%incr
Rdecrease = (154x105/%decr) − 181x103
For LM3420-12.6
Rincrease = 28x105/%incr
Rdecrease = (259x105/%decr) − 287x103
Application Circuits
For LM3420-16.8
Rincrease = 29x105/%incr
Rdecrease = (364x105/%decr) − 392x103
The circuit shown in Figure 5 performs constant-current,
constant-voltage charging of two Li-Ion cells. At the beginning of the charge cycle, when the battery voltage is less
than 8.4V, the LM3420 sources no current from the OUT pin,
keeping Q2 off, thus allowing the LM317 Adjustable voltage
regulator to operate as a constant-current source. (The
LM317 is rated for currents up to 1.5A, and the LM350 and
LM338 can be used for higher currents.) The LM317 forces
a constant 1.25V across RLIM, thus generating a constant
current of
Application Information
The LM3420 regulator/driver provides the reference and
feedback drive functions for a Lithium-Ion battery charger. It
can be used in many different charger configurations using
both linear and switching topologies to provide the precision
needed for charging Lithium-Ion batteries safely and efficiently. Output voltage tolerances better than 0.5% are possible without using trim pots or precision resistors. The cir-
ILIM = 1.25V/RLIM
DS012359-1
FIGURE 5. Constant Current/Constant Voltage Li-Ion Battery Charger
DS012359-11
FIGURE 6. Low Drop-Out Constant Current/Constant Voltage 2-Cell Charger
(approximately 5 mV). Diode D1 is also used to prevent the
battery current from flowing through the LM317 regulator
from the output to the input when the DC input voltage is removed.
As the battery charges, its voltage begins to rise, and is
sensed at the IN pin of the LM3420. Once the battery voltage
reaches 8.4V, the LM3420 begins to regulate and starts
sourcing current to the base of Q2. Transistor Q2 begins
Transistor Q1 provides a disconnect between the battery
and the LM3420 when the input voltage is removed. This
prevents the 85 µA quiescent current of the LM3420 from
eventually discharging the battery. In this application Q1 is
used as a low offset saturated switch, with the majority of the
base drive current flowing through the collector and crossing
over to the emitter as the battery becomes fully charged. It
provides a very low collector to emitter saturation voltage
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12
stage of the LM10C will disconnect the battery from the
charger circuit when the input supply voltage is removed to
prevent the battery from discharging.
(Continued)
controlling the ADJ. pin of the LM317 which begins to regulate the voltage across the battery and the constant voltage
portion of the charging cycle starts. Once the charger is in
the constant voltage mode, the charger maintains a regulated 8.4V across the battery and the charging current is dependent on the state of charge of the battery. As the cells approach a fully charged condition, the charge current falls to a
very low value.
Figure 6 shows a Li-Ion battery charger that features a dropout voltage of less than one volt. This charger is a
constant-current, constant-voltage charger (it operates in
constant-current mode at the beginning of the charge cycle
and switches over to a constant-voltage mode near the end
of the charging cycle). The circuit consists of two basic feedback loops. The first loop controls the constant charge current delivered to the battery, and the second determines the
final voltage across the battery.
With a discharged battery connected to the charger, (battery
voltage is less than 8.4V) the circuit begins the charge cycle
with a constant charge current. The value of this current is
set by using the reference section of the LM10C to force 200
mV across R7 thus causing approximately 100 µA of emitter
current to flow through Q1, and approximately 1 mA of emitter current to flow through Q2. The collector current of Q1 is
also approximately 100 µA, and this current flows through
R2 developing 50 mV across it. This 50 mV is used as a reference to develop the constant charge current through the
current sense resistor R1.
The constant current feedback loop operates as follows. Initially, the emitter and collector current of Q2 are both approximately 1 mA, thus providing gate drive to the MOSFET
Q3, turning it on. The output of the LM301A op-amp is low.
As Q3’s current reaches 1A, the voltage across R1 approaches 50 mV, thus canceling the 50 mV drop across R2,
and causing the op-amp’s output to start going positive, and
begin sourcing current into R8. As more current is forced into
R8 from the op-amp, the collector current of Q2 is reduced
by the same amount, which decreases the gate drive to Q3,
to maintain a constant 50 mV across the 0.05Ω current sensing resistor, thus maintaining a constant 1A of charge current.
The current limit loop is stabilized by compensating the
LM301A with C1 (the standard frequency compensation
used with this op-amp) and C2, which is additional compensation needed when D3 is forward biased. This helps speed
up the response time during the reverse bias of D3. When
the LM301A output is low, diode D3 reverse biases and prevents the op-amp from pulling more current through the emitter of Q2. This is important when the battery voltage reaches
8.4V, and the 1A charge current is no longer needed. Resistor R5 isolates the LM301A feedback node at the emitter of
Q2.
The battery voltage is sensed and buffered by the op-amp
section of the LM10C, connected as a voltage follower driving the LM3420. When the battery voltage reaches 8.4V, the
LM3420 will begin regulating by sourcing current into R8,
which controls the collector current of Q2, which in turn reduces the gate voltage of Q3 and becomes a constant voltage regulator for charging the battery. Resistor R6 isolates
the LM3420 from the common feedback node at the emitter
of Q2. If R5 and R6 are omitted, oscillations could occur during the transition from the constant-current to the
constant-voltage mode. D2 and the PNP transistor input
DS012359-12
FIGURE 7. High Efficiency Switching Regulator
Constant Current/Constant Voltage 2-Cell Charger
DS012359-13
FIGURE 8. Low Dropout Constant Current/Constant
Voltage Li-Ion Battery Charger
A switching regulator, constant-current, constant-voltage
two-cell Li-Ion battery charging circuit is shown in Figure 7.
This circuit provides much better efficiency, especially over a
wide input voltage range than the linear topologies. For a 1A
charger an LM2575-ADJ. switching regulator IC is used in a
standard buck topology. For other currents, or other packages, other members of the SIMPLE SWITCHER™ buck
regulator family may be used.
Circuit operation is as follows. With a discharged battery
connected to the charger, the circuit operates as a constant
current source. The constant-current portion of the charger is
formed by the loop consisting of one half of the LM358 op
amp along with gain setting resistors R3 and R4, current
sensing resistor R5, and the feedback reference voltage of
1.23V. Initially the LM358’s output is low causing the output
of the LM2575-ADJ. to rise thus causing some charging current to flow into the battery. When the current reaches 1A, it
is sensed by resistor R5 (50 mΩ), and produces 50 mV. This
50 mV is amplified by the op-amps gain of 25 to produce
13
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Application Circuits
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Application Circuits
The circuit in Figure 8 is very similar to Figure 7, except the
switching regulator has been replaced with a low dropout linear regulator, allowing the input voltage to be as low as 10V.
The constant current and constant voltage control loops are
the same as the previous circuit. Diode D2 has been
changed to a Schottky diode to provide a reduction in the
overall dropout voltage of this circuit, but Schottky diodes
typically have higher leakage currents than a standard silicon diode. This leakage current could discharge the battery
if the input voltage is removed for an extended period of
time.
Another variation of a constant current/constant voltage
switch mode charger is shown in Figure 9. The basic feedback loops for current and voltage are similar to the previous
circuits. This circuit has the current sensing resistor, for the
constant current part of the feedback loop, on the positive
side of the battery, thus allowing a common ground between
the input supply and the battery. Also, the LMC7101 op-amp
is available in a very small SOT23-5 package thus allowing a
very compact pc board design. Diode D4 prevents the battery from discharging through the charger circuitry if the input
voltage is removed, although the quiescent current of the
LM3420 will still be present (approximately 85 µA).
(Continued)
1.23V, which is applied to the feedback pin of the
LM2575-ADJ. to satisfy the feedback loop.
Once the battery voltage reaches 8.4V, the LM3420 takes
over and begins to control the feedback pin of the
LM2575-ADJ. The LM3420 now regulates the voltage across
the battery, and the charger becomes a constant-voltage
charger. Loop compensation network R6 and C3 ensure
stable operation of the charger circuit under both
constant-current and constant-voltage conditions. If the input
supply voltage is removed, diode D2 and the PNP input
stage of the LM358 become reversed biased and disconnects the battery to ensure that the battery is not discharged.
Diode D3 reverse biases to prevent the op-amp from sinking
current when the charger changes to constant voltage mode.
The minimum supply voltage for this charger is approximately 11V, and the maximum is around 30V (limited by the
32V maximum operating voltage of the LM358). If another
op-amp is substituted for the LM358, make sure that the input common-mode range of the op-amp extends down to
ground so that it can accurately sense 50 mV. R1 is included
to provide a minimum load for the switching regulator to assure that switch leakage current will not cause the output to
rise when the battery is removed.
DS012359-14
FIGURE 9. High Efficiency Switching Charger
with High Side Current Sensing
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14
(Continued)
DS012359-15
FIGURE 10. (Fast) Pulsed Constant Current 2-Cell Charger
15
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LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Application Circuits
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
Application Circuits
off time will be very short (1 ms or less), but when the battery
approaches full charge, the off time will begin increasing to
tens of seconds, then minutes, and eventually hours.
(Continued)
A rapid charge Lithium-Ion battery charging circuit is shown
in Figure 10. This configuration uses a switching regulator to
deliver the charging current in a series of constant current
pulses. At the beginning of the charge cycle
(constant-current mode), this circuit performs identically to
the previous LM2575 charger by charging the battery at a
constant current of 1A. As the battery voltage reaches 8.4V,
this charger changes from a constant continuous current of
1A to a 5 second pulsed 1A. This allows the total battery
charge time to be reduced considerably. This is different
from the other charging circuits that switch from a constant
current charge to a constant voltage charge once the battery
voltage reaches 8.4V. After charging the battery with 1A for 5
seconds, the charge stops, and the battery voltage begins to
drop. When it drops below 8.4V, the LM555 timer again
starts the timing cycle and charges the battery with 1A for another 5 seconds. This cycling continues with a constant 5
second charge time, and a variable off time. In this manner,
the battery will be charged with 1A for 5 seconds, followed by
an off period (determined by the battery’s state of charge),
setting up a periodic 1A charge current. The off time is determined by how long it takes the battery voltage to decrease
back down to 8.4V. When the battery first reaches 8.4V, the
The constant-current loop for this charger and the method
used for programming the 1A constant current is identical to
the previous LM2575-ADJ. charger. In this circuit, a second
LM3420-8.4 has its VREG increased by approximately
400 mV (via R2), and is used to limit the output voltage of the
charger to 8.8V in the event of a bad battery connection, or
the battery is removed or possibly damaged.
The LM555 timer is connected as a one-shot, and is used to
provide the 5 second charging pulses. As long as the battery
voltage is less than the 8.4V, the output of IC3 will be held
low, and the LM555 one-shot will never fire (the output of the
LM555 will be held high) and the one-shot will have no effect
on the charger. Once the battery voltage exceeds the 8.4V
regulation voltage of IC3, the trigger pin of the LM555 is
pulled high, enabling the one shot to begin timing. The
charge current will now be pulsed into the battery at a 5 second rate, with the off time determined by the battery’s state
of charge. The LM555 output will go high for 5 seconds (pulling down the collector of Q1) which allows the 1A
constant-current loop to control the circuit.
DS012359-16
FIGURE 11. MOSFET Low Dropout Charger
Figure 11 shows a low dropout constant voltage charger using a MOSFET as the pass element, but this circuit does not
include current limiting. This circuit uses Q3 and a Schottky
diode to isolate the battery from the charging circuitry when
the input voltage is removed, to prevent the battery from discharging. Q2 should be a high current (0.2Ω) FET, while Q3
can be a low current (2Ω) device.
Note: Although the application circuits shown here have
been built and tested, they should be thoroughly evaluated with the same type of battery the charger will eventually be used with.
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Different battery manufacturers may use a slightly different battery chemistry which may require different
charging characteristics. Always consult the battery
manufacturer for information on charging specifications
and battery details, and always observe the manufacturers precautions when using their batteries. Avoid overcharging or shorting Lithium-Ion batteries.
16
LM3420-4.2, -8.2, -8.4, -12.6, -16.8 Lithium-Ion Battery Charge Controller
Physical Dimensions
inches (millimeters) unless otherwise noted
5-Lead Small Outline Package (M5)
For Ordering Information See Figure 1 In This Data Sheet
NS Package Number MF05A
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